1. Field of the Invention
This invention relates to electronic phase scan antennas for operation in the millimeter wave region of the frequency spectrum and more particularly to a microstrip phase scan antenna array for planar radar scanning in a single plane with a substantially pencil-shaped beam. 2. Description of the Prior Art
Radar system antennas are customarily designed to be scanned in two, orthogonally-related planes, such as azimuth and elevation, for example. However, for certain applications, the antenna need only be scanned in a single plane because other means are available to provide scanning in the orthogonally-related plane. For example, if an antenna capable of scanning only in a single plane is mounted in a moving vehicle, such as an aircraft, a terminally-guided weapon or a remotely-piloted vehicle, and if the motion or track of the vehicle is along a path which is orthogonally-related to the scanning plane of the antenna, then scanning is effectively provided in two, orthogonally-related planes.
Since such single plane scanning antennas are often mounted in the moving vehicle itself, the size and weight of the antenna and its associated scanning system becomes very important. For example, when such antennas are used in aircraft, terminally-guided weapons and remotely-piloted vehicles, it is essential that the antenna and its scanning system be as compact as possible and of extremely small size and low weight. The antenna system should also be capable of being fabricated at a reasonable cost. Furthermore, for some applications, such as terminally-guided weapons, for example, it is desirable that the antenna system be conformal because conformal antennas can be bent or deformed to some degree to facilitate their mounting and placement in the limited space usually available in weapons of this type. Also of value for use in terminally-guided weapons of certain types are antenna arrays and associated scanning systems which are frangible because in these types of weapons, the antenna systems must be so mounted in the body of the guided weapon that it is directly in the path of a small projectile or charge which is fired through the antenna system before the impact of the weapon with the target.
Because of the aforementioned limitations, antenna systems which are mechanically scanned or driven are usually not feasible. Similarly, the electronically "steered" phase array systems which have been developed which do not rely upon mechanical scanning or drive mechanisms are generally very complex and bulky because a large number of phase shifting circuits are required for the individual antenna elements making up the array. With the advent of planar type circuitry which operates in the millimeter wave region of the frequency spectrum, microstrip antenna arrays have been developed which satisfy not only the aforementioned size and weight limitations but are also conformal and frangible. Unfortunately, however, the phase shifting circuits which must be employed to "steer" or scan the array are not available in microstrip circuitry.